1. Field of the Invention
The present invention relates to a mobile communication terminal. More particularly, the present invention relates to an apparatus and a method for increasing an output efficiency of a mobile communication terminal.
2. Description of the Related Art
As a mobile communication technology evolves, a communication system processes a signal of a higher data rate gradually and requires a broadband transmission signal and a complicated modulation scheme. Accordingly, a transceiver of a mobile communication terminal should include a high efficiency, a broadband signal processing capability, and a linear amplify characteristic in order to process a broadband signal and a signal of a high Peak to Average Power Ratio (PAPR).
To accomplish the above characteristics, a mobile communication terminal uses a polar modulation power amplifier.
The polar modulation power amplifier separates the phase component and the envelope component of an input signal. After that, the phase component is up-converted to an RF carrier and provided as an input signal of the power amplifier. Also, the envelope component is modulated by a supply modulator and provided as a power source of a collector/drain of the power amplifier. Accordingly, the power amplifier amplifies the up-converted phase component provided via an input end using the modulated envelop component provided via the collector/drain to maintain a high efficiency and linearity of a high PAPR signal.
As described above, the power amplifier modulates the amplitude of an RF signal (AM modulation) using output power modulated by the supply modulator. Accordingly, the linearity of the supply modulator has a direct influence on the quality of a signal output via the power amplifier. Also, the efficiency of the entire system is determined by the product of the efficiency of the supply modulator and the efficiency of the power amplifier.
FIG. 1 illustrates the configuration of the conventional supply modulator.
As illustrated in FIG. 1, the supply modulator 100 has a hybrid form including a voltage regulator 102 and a switching regulator 104.
The voltage regulator 102 controls a voltage to be amplified in direct proportion to an input signal and output to determine an output voltage of the supply modulator 100.
The switching regulator 104 supplies an output current.
Generally, the voltage regulator 102 can linearly convert a signal in a wide band but has a low efficiency. The switching regulator 104 has a very high efficiency but cannot process a signal in a wide band. Accordingly, the supply modulator 100 determines the linearity of an output signal of the supply modulator 100 according to the high linearity of the voltage regulator 102, and determines the efficiency of the output power of the supply modulator 100 according to the high efficiency characteristic of the switching regulator 104.
However, since the battery capacity of a mobile communication terminal is limited, an output voltage of the supply modulator 100 determined by the voltage regulator 102 of the mobile communication terminal may be limited depending on an amount of the battery of the mobile communication terminal.
In the case where a battery voltage available at the voltage regulator 102 is limited, the quality of an output signal in a high power mode in which a transmitter consumes maximal power may deteriorate.